Thermal polymerization of styrene is known using a disulfide modifier in the presence of azoisobutyronitrile initiator (Pierson et al, 17 J. Polymer Science 221-246, 1955). Alkyl disulfides were found in the latter reference to be relatively ineffective compared to aryl disulfides in incorporating end groups into polystyrene. U.S. Pat. No. 3,470,146 discloses improved polystyrene beads produced by thermal polymerization of styrene in the presence of a finely divided phosphate suspending agent, a water soluble sulfite or precursor, and certain water soluble organic sulfides. None of the above references discloses liquid polymers or a process for preparing them, let alone hydroxyl-containing liquid polymers having an aliphatic polymer backbone and sulfide linkages near the terminal portions of the polymer molecule, and the use of ultraviolet radiation to prepare the polymers. Such new hydroxyl-containing liquid polymers and a process for preparing them are desired.